1. Field of the Invention
The present invention relates to a resilient prosthetic foot that has a reinforcement member to provide reinforcement, and has multiple forefoot members to simulate toe rotation. More particularly, the present invention relates to a prosthetic foot having at least two resilient forefoot members, at least one resilient heel member, and at least one resilient reinforcement member that is engaged after the forefoot or heel members move from a normal range of movement to an extreme range.
2. Prior Art
Many individuals have lost a limb for various reasons including war, accident, or disease. In most instances these individuals are not only able to live relatively normal lives, but physically active lives as well. Often times, these individuals are aided in their everyday lives by a prosthetic limb. The objective of prosthesis is to provide an artificial limb that simulates the function and natural feel of the replaced limb.
With respect to prosthetic feet, the development of a functional and natural artificial foot has been limited only by material and imagination. Many designs have attempted to copy the anatomy of the foot or simulate its actions by replacing the bones and muscle with various mechanical components. Other designs have departed radically from mere anatomical copying or mechanical simulation by replacing the entire foot with an energy storage element such as a spring. As the user steps onto the foot, the user's weight compresses the spring. As the user moves forward, the user's weight comes off the foot and the energy stored in the spring is used to propel the user forward.
Examples of such energy storing, spring-like feet having a forefoot member and a heel member include U.S. Pat. Nos. 5,037,444 and 4,547,913. U.S. Pat. No. 5,037,444 issued Aug. 6, 1991 to Phillips discloses a prosthetic foot having a forefoot portion and a heel portion. The forefoot portion has an attachment section, a curvilinear spring section, an arch section, and a toe section formed integrally with one another. The heel portion is removably attached to the forefoot portion at the intersection of the arch and toe sections by a bolt and nut. An elastomeric wedge is inserted between the forefoot portion and the heel portion. U.S. Pat. No. 4,547,913 issued Oct. 22, 1985 to Phillips discloses a prosthetic foot having a forefoot portion and a heel portion. The forefoot portion and the heel portion are bound together with a "resin impregnated filament binding" by winding the filament around the members.
The stiffness of prosthetic feet typically vary according to the intended use. Feet intended for everyday use typically require a soft feel and thus incorporate a loose spring. Feet intended for athletic use typically require strength and thus incorporate a stiff spring. Although different feet may be changed to suit the particular activity, such switching is inconvenient and at times it is impossible, such as a sudden need to run to catch, or avoid being hit by, a bus. Feet designed for particular purposes are typically unsuited for other purposes. Stiff, athletic feet are too hard for everyday use, and loose, everyday feet are too fragile for athletic use. Multiple-use feet have been designed which are capable of many different uses, but without being particularly well suited for any use.
In addition, the performance of these energy storing feet has been altered in various ways, such as by using multiple springs in various configurations, using bladders or resilient materials disposed between various elements, and using multiple springs that deflect at different intervals of foot deflection to add resistance.
U.S. Pat. No. 5,290,319 issued Mar. 1, 1994 to Phillips discloses a prosthetic foot having a forefoot portion, a heel portion, and an auxiliary member disposed above the forefoot portion. A bladder is disposed between the auxiliary member and the forefoot portion. The pressure in the bladder is varied to adjust the performance of the foot. In this configuration, the auxiliary member is a structural member against which the bladder is compressed.
U.S. Pat. No. 5,387,246 issued Feb. 7, 1995 to Phillips discloses a prosthetic foot having a forefoot portion, a sole member, and an auxiliary or secondary stiffness member disposed above the forefoot portion. The secondary member adds stiffness to the foot when the foot is deflected sufficiently forward such as to engage the secondary member.
U.S. Pat. No. 4,721,510 issued Jan. 26, 1988 to Cooper et al. discloses a prosthetic foot having a relatively flexible primary foot member and a relatively stiff secondary foot member disposed above the primary foot member such that the spring force of the foot is increased as the primary foot member deflects to the secondary foot member.
One problem with all these configurations is that the foot forms a unitary member incapable of providing independent and multiple responses to uneven terrain, such as a slope. The unitary member is a platform that must rotate as a single body to conform to the slope of the terrain in an unnatural manner. Such a foot is incapable of rotating about a longitudinal axis.
Almost all of the past designs have focused on the major aspect of the prosthetic foot--movement of the ankle or foot as it relates to walking or running. Few designs consider the workings of the toes or the less conspicuous movements of the foot and ankle, such as the rotation of the foot and toes when the user stands on an incline. In a natural foot, the foot and toes rotate to conform to the slope of the terrain. The artificial foot of previous designs usually incorporates a unitary foot and toe platform that is incapable of such independent rotational movement or response.
U.S. Pat. No. 2,640,200 issued Jun. 2, 1953 to Wisbrun discloses a prosthetic foot having a steel, horizontal foot plate connected to a vertical leg post by two joints. The first joint has a head mounted in a diagonally mounted cylindrical bearing such that as the foot plate rotates downward it is also rotated inward and vice versa. The second joint permits limited vertical rotation by a T-head inserted through a slot, turned, and secured by a screw. An arm, attached to the leg post, extends over the foot plate and engages an inclined leaf spring. The purpose of the above construction is a more natural gait. The resulting motion of the above construction is the rotation of the foot plate down and inward as the user steps on the heel and then rotation upward and outward as weight is taken off the foot plate. Wisbrun also discloses that a slit may be provided in the forward end of the foot plate for "a more effective resilient up-thrust" as weight is taken off the foot plate. One problem with this configuration is the complexity of the several joints. There are numerous moving parts and joints subject to friction, wear, and failure. In addition, the slit in the foot plate does not simulate toe rotation.
U.S. Pat. No. 2,036,830 issued Apr. 7, 1936 to Rowley discloses a prosthetic foot having a shin member connected to a foot member by a bearing hinge. The foot member has a solid, inner core portion and a flexible exterior. The foot member also has a rigid member with a "pair of spaced apart prongs" extending between the core and the exterior and a pivot at the ball of the foot in contact with the prongs. The rigid member is operatively attached to a rubber block that expands and contracts between the shin member and core member as the user walks. Thus, the rigid member acts as a lever extending from the toe position to the ankle position and pivoting at the ball of the feet. As the user pivots forward on the foot, the rubber block is compressed and the ankle end of the rigid member is forced down and the toe end of the rigid member is forced up. As the user lifts the foot, the rubber block expands and the ankle end of the rigid member is forced up and the toe end of the rigid member is forced down. The purpose of the rigid member is to return the flexible toe portion to its normal position after being bent upwards by walking. One problem with this configuration is that the rigid prongs do not deflect or bend to simulate toe rotation. Nor do the rigid prongs pivot independently.
Another problem with both the above devices is that neither stores a substantial amount of energy. In addition, neither has a reinforcement member to vary the stiffness of the foot.
Therefore, it would be advantageous to develop a prosthetic foot capable of simulating the natural toe rotation of a real foot. It would also be advantageous to develop a prosthetic foot having a reinforcement member. In addition, it would be advantageous to develop a prosthetic foot having various degrees of stiffness.